The present invention relates to an optical receiver and, more particularly, to an optical receiver which compensates for a phase variation due to a change in temperature of a timing extraction circuit of a tank scheme.
Generally, an optical repeater requires a 3R function, i.e., a reshaping function of converting an optical input signal into an electrical signal, amplifying the signal, and shaping the waveform of the signal, a retiming function of extracting a timing component from the signal after reshaping, and a regenerating function of identifying xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d from the signal after reshaping and regenerating it to the same signal as a transmission pulse. Japanese Patent Laid-Open No. 3-258034 discloses a technique of controlling the temperature of a SAW (Surface Acoustic Wave) filter constituting a tuning circuit necessary for extracting the timing signal for regeneration to adjust the phase of the timing signal in the optical receiver having the 3R function. This prior art will be described with reference to FIGS. 4 and 5.
Referring to FIG. 4, the optical repeater comprises an optical reception circuit 41 for converting an optical input signal into an electrical signal 45 and performing reshaping, a regenerating circuit 42 for performing regenerating for the electrical signal 45 output from the optical reception circuit 41, a timing extraction circuit 43 for extracting the phase of a transmission pulse and supplying a timing signal 46 as a clock signal to the regenerating circuit 42, and an optical transmission circuit 44 for converting an electrical signal output from the regenerating circuit 42 into an optical signal again and sending it.
The timing extraction circuit 43 must suppress the jitter of the regeneration output pulse output as the timing signal 46. For this purpose, a pulse repetitive frequency component is extracted from an equalized waveform train output from the optical reception circuit 41 by a full-wave rectifier and a tuning circuit, and then amplification limitation is performed by a limiter amplifier, thereby obtaining the timing signal 46 having a small amplitude and phase error even for a wide-range mark ratio. In addition, a SAW filter is used for the tuning circuit. By controlling the temperature of the SAW filter, the phase of the timing signal 46 is adjusted.
FIG. 5 shows the arrangement of a phase adjustment circuit incorporated in the timing extraction circuit 43 shown in FIG. 4 to control the phase of the SAW filter constituting the tuning circuit for extracting a timing signal. The phase adjustment circuit shown in FIG. 5 comprises a SAW filter 51, a Peltier device 52, and a thermister 53, which are arranged integrally with each other, and a control circuit 54 to which a reference voltage is supplied.
Since the phase of the SAW filter 51 changes in proportion to the temperature, the phase can be set at a predetermined value by controlling the temperature. When the Peltier device 52 and the thermister 53 are controlled to a temperature corresponding to an externally supplied reference voltage 55 by the control circuit 54, the temperature of the SAW filter 51 is set to ensure a predetermined phase. In this arrangement, the temperature of the SAW filter 51 is set by adjusting the reference voltage 55, so the phase of the timing signal 46 output from the timing extraction circuit 43 can be adjusted.
In the conventional phase adjustment circuit, since the Peltier device 52 is used to perform temperature compensation, the power consumption increases upon heating/cooling the Peltier device. For this reason, this phase adjustment circuit can hardly be applied to an optical receiver with a transmission rate of the order of Gbit/sec or less, for which reduction of power consumption is required. In addition, since only the output phase of the SAW filter is controlled, phase variations generated by a circuit device other than the SAW filter cannot be compensated for.
It is an object of the present invention to provide an optical receiver which compensates for a phase variation due to the ambient temperature of a timing extraction circuit in the optical receiver at a low power consumption.
It is another object of the present invention to provide an optical receiver which compensates for a phase variation due to the temperature of an entire timing extraction circuit.
In order to achieve the above object, according to the present invention, there is provided an optical receiver comprising photoelectric conversion means for converting input signal light into an electrical signal, reshaping means for amplifying the electrical signal output from the photoelectric conversion means and performing waveform shaping, regenerating means for regenerating data from an output from the reshaping means on the basis of a retiming signal, timing signal extraction means for extracting a timing signal from an output signal from the reshaping means, reference voltage generation means for generating a reference voltage changing in accordance with a variation in ambient temperature, and a comparator for comparing an output signal from the timing signal extraction means with the reference voltage output from the reference voltage generation means and supplying the retiming signal to the regenerating means.